It is conventionally common that an internal combustion engine control apparatus has a waterproof structure from waterproofness, dust resistance and rust prevention viewpoints. Mainstream waterproof structures include a waterproofing structure having tightening force by sandwiching a molded elastic member between a case and a cover, and a waterproof structure having a waterproofing adhesive applied and cured for fluid-tight sealing. As a market demand concerning waterproofness, a demand for a long life gets stronger, so that long-term reliability of the waterproof structure needs to be ensured.
Although a long life can be achieved by simply adopting material or treatment of high corrosion resistance, a resulting control apparatus is problematically very expensive. Accordingly, adopting a structure having a life extended in relation to creeping corrosion by increasing a part to which the waterproofing adhesive is adhered has become mainstream to meet the demand at low cost. In cases where the adhesive part is formed simply of a plane surface, the adhesive part enlarges, thus resulting in a control apparatus increased in size. For this reason, a structure securing an increased adhesive length by making an adhesive part uneven is adopted.
Structures such as described in Japanese Patent Unexamined Publication. No. 2000-323865 (PTL 1) and Japanese Patent Unexamined Publication No. 2013-105766 (PTL 2) are known as waterproof structures of control apparatuses in a manufacturing process of the control apparatus of PTL 1, allowances are increased for variations in the amount of adhesive applied and varying application patterns, so that a highly reliable electronic circuit case of stable quality provided (refer to paragraph 0008). This electronic circuit case is assembled by fixing a cover to a housing with an internally mounted electronic circuit substrate by bonding (refer to paragraphs 0013 to 0015). For this reason, the housing includes a fully circumferential groove in which an adhesive is filled and the cover is engaged, and at a part of the fully circumferential groove, an adjacent groove reduced in wall height. The adhesive overflowing the fully circumferential groove is allowed to flow into the adjacent groove, so that the amount of adhesive to be applied is set to be slightly larger than a minimum set amount, thereby preventing an adhesive shortage (refer to paragraphs 0016 to 0017). In the control apparatus of PTL 2, a case (housing) is constructed of a base and a cover that cover respective sides of an electronic circuit substrate, and a lid covering an opening defined by the base and the cover (refer to paragraphs 0013). The base is formed with a groove along its four sides, and a sealant is applied to the groove. When a projection provided to the cover is in the process of being inserted in the groove, the sealant is structurally pushed into a gap between the projection and a groove surface (refer to paragraphs 0014 to 0016 and FIGS. 2(a) to 2(c)). A structure described in another embodiment has a jetty formed inside a projection provided to a cover, and a cover-side groove defined by the projection and the jetty is engaged with a base-side groove (refer to paragraph 0023 and FIGS. 4(a) and 4(b)). In this structure, a sealant also flows into an inner periphery of the projection, thus resulting in an increased adhesive distance, and consequently, adhesive strength and sealability between the cover and a base increase.